/claim #71

Summary: Added focused export coverage for src/export/index.ts, CSV multiline/primitive export behavior, and JSON nested/null/serialization-failure behavior. Verification: targeted vitest export tests passed (23 tests), prettier check passed, git diff –check passed. Full vitest run currently fails on existing unrelated src/rls/index.test.ts assertions where policy WHERE clauses are not injected. AI-assisted with Codex; reviewed and scoped to the non-overlapping export coverage slice from my attempt comment.